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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    
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<script>
   // 实现trim(str)方法，过滤字符串首位空白
   function trim(str){
    var a2 = str.replace(/^\s+/g,"");
    return a2;
   }
   
   var s = trim("  31231311  ");
   console.log(s, s.length);
</script>
</html>